How much RPM for small parts

[JohnJW]

Thanks to the cncone wisdom I'm almost settled on the TL-2. However, I wonder if I need the higher rpm spindle. I plan on turning some 1/8" parts, but according to the rpm formula, SFM = PI x D x RPM / 12, the rpm for 1/8" aluminum rod with sfm of 200 will be ~6111rpm and that's 3x the maximum rpm of the standard TL-2 spindle.

The TL-2 will be a general purpose lathe so in addition to the 1/8" rods I also want to turn 2~3" tubes and may even go up 12". Is 1/8" to 12" too much of a range for the TL-2?

Should I upgrade to the 3600rpm spindle? Will the 3600rpm spindle have the same spindle bore as the 2000rpm spindle and can the standard 8" or 10" chuck hold 1/8" rods? Should I go with the 8" or 10" chuck or neither because there's a better after market solution to accommodate smaller diameter and/or higher rpm? What's the effect of 2000 rpm vs 3600 rpm for smaller diameter parts? Will slower feed compensate for the lack of rpm, and what do people usually use the 3600rpm spindle for?

Thanks again,

John

[pit202]

If we do smaller parts than 20mm I wish I had 6.000 RPM`s , that doesn`t mean you can not turn with 2k RPM`s - but if you require high quality surfaces you need to hold high surface speed - especially in low alloy steels.

[Geof]

Check the specs for the 3600rpm option and I think you will find it has the same spindle bore; I was told the only difference in the spindle are bearings with a higher speed rating.

You need to remember with a general purpose lathe you have to make some compromises at both end of the range whether it is manual or CNC. It is going to be slow for small diameter and underpowered for taking heavy cuts on large diameters.

Fpr gripping small diameters you can machine your own soft jaws either to grip the material directly, or machine the jaws to take a 5C collet and use that inside the jaws.

Alternatively you can get a 5C collet chuck and hold that in your three jaw chuck. With the Set-Tru type chucks you can get things running very true.

[Donkey Hotey]

Originally Posted by Geof Fpr gripping small diameters you can machine your own soft jaws either to grip the material directly, or machine the jaws to take a 5C collet and use that inside the jaws.

I'm sure you'll correct me if I'm wrong, but I don't know of any 10", manual scroll chucks that want to be spun harder than 1500-1800 RPM, right? If he's going to be working in sub 1" material, he'll need a dedicated 5C or 16C/3J collet closer. I never spin my 8" chuck at more than 1200-1500 RPM.

[Geof]

I will check, I have a 10" Bison and an 8"; I am pretty sure the 8" is okay above 3600 and the 10" is ?700 but I cannot remember if the ? is 2 or a 3.

[JohnJW]

Are lathe chucks something that people swap out regularly to suit different part diameters? If my starting range is from 1/8" to 2.5" in diameter what are the recommendation for the chuck or chucks?

Is 3600rpm spindle worth the extra cost? I'm guessing it's not a field installable option so it's not something that can be added later on if needed.

[Geof]

The 3600 rpm is not field installable; I asked and that is when I was told it had higher grade bearings.

I was buying a demo machine with the standard spindle at a good price and when I thought about it I decided 3600 rpm wasn't necessary for the many extra dollars I would have spent.

Mind you it does have the advantage of a higher power motor (I think).

Swapping chucks regularly is not something I do because they are heavy. I normally have the 8" on my TL2 and have only put the 10" on once in 3 years.

The only real advantage to the 10" is that you can then make use of the large spindle bore; I suggest getting the 8" with the initial purchase and when you need a bigger one get it.

[JohnJW]

Originally Posted by Geof The 3600 rpm is not field installable; I asked and that is when I was told it had higher grade bearings. I was buying a demo machine with the standard spindle at a good price and when I thought about it I decided 3600 rpm wasn't necessary for the many extra dollars I would have spent. Mind you it does have the advantage of a higher power motor (I think).

Geof,

If you have to buy the machine again today and have the option to add the 3600rpm spindle will you add it? It's also a 12hp spindle.

Does that extra 1600rpm make a big difference on smaller diameter, ie ~1/8" parts?

Thanks,

[Geof]

Would I get the 3600 rpm spindle???

I don't know.

I am not very good at hypothetical questions.

The extra rpm can be useful as pit202 mentioned, for some steels but it is possible to compensate by using high rake cutters to get a good surface finish.

Are you getting the enclosed TL2-P or the open one? To be honest the idea of a chuck doing 3600 rpm just in front of my nose makes me nervous. Not a totally rational response I agree.

[Donkey Hotey]

Originally Posted by JohnJW Are lathe chucks something that people swap out regularly to suit different part diameters? If my starting range is from 1/8" to 2.5" in diameter what are the recommendation for the chuck or chucks?

Absolutely. Chucks are workholding, just like different setups on a mill. For general parts, a few at a time, yeah, the 8" 3-jaw is your best compromise. That'll get you started but sooner or later, you're going to have a small part where you're working too close to the chuck and tools won't clear easily or it can't hold things as true as you want them or whatever.

For general and widely varied work:

• 8" 3-Jaw
• 5C Collet nose with the closing method of your preference
• 8 or 10" 4-Jaw
• Maybe even a 10" faceplate (depending on the type of work you do)

Don't forget your tailstock. A basic live center is nice but I quickly realized that while it was fine for manual work, it was too bulky to program around. That's when I discovered why they make extended-point CNC live centers. Of course some parts will need a bull-nose center. Then there are parts that are too big for that, or too awkward or whatever. That's when you start looking at the Bison rotating tailstock chucks. If I had to replace my current tailstock tooling, it would probably cost more than $2,000 (Bison rotating chucks just got very expensive for some reason).

None of this is relevant to your original question about the spindle speed, but it may have crossed your mind. Every machine and every piece of tooling you choose, no matter how much you spend, will have compromises.

[Geof]

Originally Posted by Donkey Hotey 8" 3-Jaw 5C Collet nose with the closing method of your preference 8 or 10" 4-Jaw Maybe even a 10" faceplate (depending on the type of work you do)

He's a lot younger than me which is why he doesn't mind switching these things back and forth.

[Donkey Hotey]

Originally Posted by Geof He's a lot younger than me which is why he doesn't mind switching these things back and forth.

Oh, you bet that I mind. For the first time, I now keep a butterfly air impact wrench by the lathe.